1. Field of the Invention
The present invention relates to carburetors and, particularly, to carburetors for small internal combustion engines of the type used with lawn mowers, lawn tractors, and small implements, as well as sport vehicles.
2. Description of the Related Art
Small internal combustion engines typically include a carburetor, which provides an air-fuel combustion mixture to the engine. One type of carburetor commonly used in small engines includes a fuel bowl for storing fuel and a throat with a venturi region through which air is drawn and into which fuel is drawn for mixing with the intake air. When the pressure in the fuel bowl is greater than the pressure in the venturi region, as is the case when the engine is running, fuel is drawn from the fuel bowl and conveyed through a conduit to the venturi region where it is mixed with air and supplied to the engine.
When the engine is at rest, the pressure in the fuel bowl is not greater than the pressure in the venturi region, and therefore, fuel is not drawn from the fuel bowl into the venturi region. In order to start the engine, the carburetor must be primed so that an adequate air-fuel mixture is supplied to the engine. Typically, to prime the engine, the fuel bowl is pressurized to force an amount of priming fuel from the fuel bowl into the venturi region to provide an enriched air/fuel mixture for engine starting.
One primer system includes a resilient primer bulb or bellows that, when manually depressed, increases the pressure in the fuel bowl, causing an amount of priming fuel to flow from the fuel bowl through a nozzle into the carburetor throat. In some of these systems, the primer bulb itself also serves as a check valve to seal off an internal vent passage within the carburetor, such that air within a priming chamber is directed into the fuel bowl to pressurize the fuel bowl.
The foregoing priming systems require an operator to manually depress a priming bulb which may present potential problems. For instance, if the operator does not depress the bulb completely, the resulting pressure in the fuel bowl may be inadequate to cause a sufficient amount of fuel to flow into the throat. In addition, the primer bulb is most effective as a check valve when it is depressed directly inwardly toward the carburetor along a straight line. If the operator depresses the bulb at an angle, the bulb may not effectively seal off the internal vent passage, allowing air to leak into the internal vent passage such that the fuel is not pressurized sufficiently to provide priming fuel to the carburetor throat in an amount effective for engine starting. Thus, multiple depressions of the primer bulb may be requried.
A number of other primer systems use a primer bulb to introduce liquid fuel directly into the carburetor throat. In these systems, fuel is drawn into the primer bulb when the bulb is depressed and released. When the primer bulb is depressed again, the fuel contained in the primer bulb is forced from the bulb to the throat. This system poses similar disadvantages. If the primer bulb is not depressed completely, the fuel injected from the bulb to the throat may be insufficient to start the engine.
Other primer systems have been developed which include complex electronic devices that sense engine temperature and fuel line pressure. When a certain threshold is sensed, the electronic primer advises the user to terminate manual priming. However, the inclusion of electronic devices in a priming system significantly increases the manufacturing costs of the priming system.
It is desired to provide a primer system for small engine carburetors that is an improvement over the foregoing.